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Challenge

Project-1: Powertrain for aircraft in runways

VVasanth Teja30 Jun 2021
DESIGN

AIM:

  1. SEARCH AND LIST OUT THE TOTAL WEIGHT OF VARIOUS TYPES OF AIRCRAFT.
  2. DIFFERENCE BETWEEN GROUND SPEED AND AIRSPEED?
  3. WHY IS IT NOT RECOMMENDED TO USE AIRCRAFT ENGINE POWER TO MOVE IT ON THE GROUND AT THE AIRPORT?
  4. HOW AN AIRCRAFT IS PUSHED TO THE RUNWAY WHEN IT IS READY TO TAKE OFF?
  5. LEARN ABOUT TAKE-OFF POWER, TYRE DESIGN, ROLLING RESISTANCE, TYRE PRESSURE, BRAKE FORCES WHEN LANDING.
  6. TAKE SOME NECESSARY ASSUMPTIONS AND CALCULATE THE FORCE AND POWER REQUIRED TO PUSH AND PULL AN AIRCRAFT BY A TOWING VEHICLE.
  7. DESIGN AN ELECTRIC POWERTRAIN WITH THE TYPE OF MOTOR, ITS POWER RATING, AND ENERGY REQUIREMENT TO FULFILL AIRCRAFT TOWING APPLICATION.
    • ESTIMATE THE DUTY CYCLE RANGE TO CONTROL THE AIRCRAFT SPEED FROM ZERO TO HIGHEST.
    • MAKE ALL REQUIRED ASSUMPTIONS.
    • PREPARE A TABLE OF ASSUMED PARAMETERS.
    • DRAW A BLOCK DIAGRAM OF THE POWERTRAIN.

OBJECTIVE:

INTRODUCTION:

QUESTION-1:

  • SEARCH AND LIST OUT THE TOTAL WEIGHT OF VARIOUS TYPES OF AIRCRAFT.

ANSWER-1:

  1. AIRCRAFT TOTAL WEIGHT (AIRCRAFT GROSS WEIGHT)
    • The aircraft gross weight is also known as the All-up weight and abbreviated AUW is the total weight at any moment during the flight or ground operation.
    • An aircraft's gross weight will decrease during a flight due to fuel and oil consumption. An aircraft's gross weight may also vary during a flight due to payload dropping or In-flight refueling.
    • At the moment of releasing its brakes, the gross weight of an aircraft is equal to its takeoff weight. during flight, an aircraft,s gross weight is referred to as the en-route weight or in-flight weight.
      • DESIGN WEIGHT LIMITS are as follows,
        • MAXIMUM DESIGN TAXI WEIGHT ( MDTW)
        • MAXIMUM DESIGN TAKEOFF WEIGHT (MDTOW)
        • MAXIMUM DESIGN LANDING WEIGHT (MDLW)
        • MAXIMUM DESIGN ZERO-FUEL WEIGHT (MDZFW)
        • MAXIMUM FLIGHT WEIGHT (WFW)
      • AUTHORISED WEIGHT LIMITS are as follows,
        • MAXIMUM TAXI WEIGHT (MTW)
        • MAXIMUM TAKEOFF WEIGHT (MTOW)
        • MAXIMUM LANDING WEIGHT (MLW)
        • MAXIMUM ZERO-FUEL WEIGHT (MZFW)
  2. STRUCTURAL DESIGN WEIGHTS
    1. An aircraft's gross weight is limited by several weight restrictions to avoid overloading its structure or to avoid unacceptable performance or handling qualities while in operation.
    2. The absolute maximum weight capabilities of a given aircraft are referred to as the structural weight limits. The structural weight limits are based on aircraft maximum structural capability and define the envelope for the CG charts.
    3. An aircraft's structural weight capability is typically a function of when the aircraft was manufactured, and in some cases, old aircraft can have their structural weight capability increased by structural modifications.
      1. MAXIMUM DESIGN TAXI WEIGHT ( MDTW)
        • The maximum design taxi weight is also known as the maximum design ramp weight (MDRW) is the maximum weight certificated for aircraft maneuvering on the ground (taxiing or towing) as limited by aircraft strength and airworthiness requirements.
      2. MAXIMUM DESIGN TAKEOFF WEIGHT (MDTOW)
        • The maximum design takeoff weight is the maximum certificated design weight when the brakes are released for takeoff and they are the greatest weight for which compliance with the relevant structural and engineering requirements has been demonstrated by the manufacturer.
      3. MAXIMUM DESIGN LANDING WEIGHT (MDLW)
        • The maximum certificated design weight at which the aircraft meets the appropriate landing certification requirements. It generally depends on the landing gear strength or the landing impact loads on certain parts of the wing structure.
        • The maximum landing weight is typically designed for 10 feet per second (600 feet per minute) sink rate at touch down with no structural damage.
        • The maximum design landing weight (MDLW) must not exceed the maximum design takeoff weight (MDTOW).
      4. MAXIMUM DESIGN ZERO-FUEL WEIGHT (MDZFW)
        • The maximum certificated design weight of the aircraft less all usable fuel and other specified usable agents (engine injection fluid, and other consumable propulsion agents). It is the maximum weight permitted before usable fuel and other specified usable fluids are loaded in specified sections of the airplane.
        • The maximum design zero fueling weight (MDZFW) is limited by strength and airworthiness requirements. The subsequent addition of fuel will not result in the aircraft design strength being exceeded at this weight.
        • The weight difference between the maximum design takeoff weight (MDTOW) and the maximum design zero fueling weight (MDZFW) may be utilized only for the addition of fuel.
      5. MAXIMUM FLIGHT WEIGHT (WFW)
        • Minimum certificated weight for flight as limited by aircraft strength and airworthiness requirements.
  3. AUTHORISED WEIGHT LIMITS:
    1. Aircraft authorized gross weight limits are also referred to as certified weight limits are laid down in the aircraft flight manuals (AFM) and associated certificate of airworthiness. The authorized or permitted limits may be equal to or lower than the structural design weight limits.
    2. The authorized weight limits that can legally be used by an operator or airline are those listed in the AFM and the weight and balance manual.
    3. Maximum weights established, for each aircraft, by design and certification must not be exceeded
      1. During Aircraft, the operation is as follows,
        • Ramp or Taxying.
        • Takeoff.
        • En-route flight.
        • Approach.
        • Landing.
      2. During Aircraft, the loading is as follows,
        • Zero Fuel Conditions.
        • Center of Gravity Position.
        • Weight Distribution.
    4. AUTHORISED WEIGHT LIMITS are as follows,
      • MAXIMUM TAXI WEIGHT (MTW)
      • MAXIMUM TAKEOFF WEIGHT (MTOW)
      • MAXIMUM LANDING WEIGHT (MLW)
      • MAXIMUM ZERO-FUEL WEIGHT (MZFW)
        • The maximum permissible weight of the aircraft less all usable fuel and other specified usable agents (engine injection fluid, and other consumable propulsion agents).
        • It is the maximum weight permitted before usable fuel and other specified usable fluids are loaded in specified sections of the airplane.
  4. LIST OUT THE TOTAL WEIGHT OF VARIOUS TYPES OF AIRCRAFT:

QUESTION-2:

  • DIFFERENCE BETWEEN GROUND SPEED AND AIRSPEED?

ANSWER-2:

  • GROUND SPEED:
    • When traveling by car, the speed of the car is being measured relative to the ground is called ground speed.
    • Ground speed is a calculated quantity. It is calculated from the plane's airspeed and wind velocity.
    • In NO-WIND condition the aircraft speed would be measured relative to the ground, So the distance travel per unit of time would also be the same.
    • In WIND condition the air moves therefore even though the aircraft is flying at the same speed, the distance travel relative to the ground will be different.
      • In other words, speed relative to the ground will differ from the speed relative to the air.
  • AIRSPEED:
    • There are many airspeed types, but the speed that corresponds to the movement relative to the air is called True Air Speed (TAS).
    • Airspeed is a measured quantity, it's measured with the help of an instrument called PITOT TUBE.
    • PITOT TUBE - it works on Bernoulli's principle, PITOT TUBE is an instrument it helps to measure the airspeed of an aircraft and not its ground speed. Essentially it measures the speed of the wind surrounding the aircraft, which is the same as the speed of the aircraft related to the wind.
    • HERE,
      • `V_(p/g) =`Velocity of plane related to the ground speed.
      • `V_(p/w)=`Velocity of plane related to the wind.
      • `V_(w/g)=`Velocity of the wind.
        • In case of wind blowing from the TAIL or also know as TAILWIND:
          • The vehicle on the ground will need more speed to reach the same distances as with aircraft because the aircraft gets some help from the wind.
          • In TAILWIND condition:
            • GROUND SPEED = TRUE AIRSPEED + WIND COMPONENT
        • In case of wind blowing from the HEAD or also know as HEADWIND:
          • While having the headwind the vehicle would need less speed than the aircraft traveling the same distance because of the wind blowing from the aircraft head.
          • In HEADWIND condition:
            • GROUND SPEED = TRUE AIRSPEED - WIND COMPONENT

QUESTION-3:

  • WHY IS IT NOT RECOMMENDED TO USE AIRCRAFT ENGINE POWER TO MOVE IT ON THE GROUND AT THE AIRPORT?

ANSWER-3:

  • TAXIING:
    • Taxiing is the movement of an aircraft on the ground, under its own power, in contrast to Towing or Pushback where the aircraft is moved by a TUG. The aircraft usually moves on wheels, but the term also includes aircraft with Skis or Floats.
  • WHY IS IT NOT RECOMMENDED TO USE AIRCRAFT ENGINE POWER TO MOVE IT ON THE GROUND AT THE AIRPORT?
    • The Jet aircraft has the potential to reverse out of the gate themselves. But there would be a huge risk of Jet blasts because of surrounding buildings and personnel damage.
    • In the case of Low engine aircraft, It could likely be picking up gravel and all kinds of things from the ground and then pushing it sucking the dust material into the engines and it could be Damage the engine.
    • In the case of High mounted engines Pushing the aircraft to the Taxiway is the problem of not seeing what's behind the aircraft's rare area and some Associated risk with it.
  • CONCLUSION:
    • So That's where pushback Trucks or Pushback Tractors come to place for Not recommended to use aircraft engine power to move it on the ground at the airport.

QUESTION-4:

  • HOW AN AIRCRAFT IS PUSHED TO THE RUNWAY WHEN IT IS READY TO TAKE OFF?

ANSWER-4:

HOW AN AIRCRAFT IS PUSHED TO THE RUNWAY AND WHY IT IMPLEMENTED?

  • At the beginning of passenger Transport, the aircraft tended to come in after landing into the apron and it will just park close to the terminal building but not so close that it couldn't make it. A turn out again
  • This type is still happening on some smaller airports, but as the airline business started to grow and it started getting bigger hubs near the major cities the airports there started having problems with fitting aircraft onto the parking, enabling slots basically.
  • So it started looking into what if get the aircraft to just taxi straight into the gate park, fill up the passengers, and get some kind of vehicle to help the aircraft to push out and get them Taxing again.
  • Since aircraft couldn't do the power back themselves, they needed some kind of vehicle to help the aircraft push out and get them Taxing again.

QUESTION-5:

  • WHEN LANDING LEARN ABOUT THESE PARAMETERS,
    1. TAKE-OFF POWER
    2. TYRE DESIGN
    3. ROLLING RESISTANCE
    4. TYRE PRESSURE
    5. BRAKE FORCES

ANSWER-5:

  1. TAKE-OFF POWER:
    • Take-off is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne.
    • Aircraft can have different ways to take off and land. Conventional airplanes accelerate along the ground until sufficient lift is generated for take-off, and reverse the process to land.
  2. Types of TAKE-OFF's
    • There are Two Types of Take-offs,
      1. Vertical Take-Off
        • The aircraft traveling vertically, this is known as liftoff.
      2. Horizontal Take-Off
        • The aircraft that take off horizontally, usually involves starting with a transition from moving along the ground on a runway.
        • For example; balloons, helicopters, and some specialized fixed-wing aircraft (VTOL aircraft such as the Harrier),
        • no runway is needed.
  3. Performance of Take-off:
    • The takeoff distance consists of two parts, the ground run, and the distance from where the vehicle leaves the ground until it reaches 50 ft (or 15 m).
    • The sum of these two distances is considered the takeoff distance. The takeoff distance is generally calculated for maximum weight in a standard atmosphere. usually, the worst-case scenario is also calculated which is maximum weight, high altitude, and a standard “hot” day.
      • The calculation of the ground roll to Tak-Off:
        • In order to calculate the ground roll, we need to write the equations of motion for the vehicle as it moves down the runway.
            • A free-body diagram of the vehicle is shown to the right. The forces that act on it are
              • The aerodynamic forces of lift and drag (L and D),
              • The thrust force (T),
              • The ground normal force (R) and
              • The ground friction force (`muR`), where `muR` is the coefficient of rolling friction.
      • We can now write the equations of motion along the runway and perpendicular to it.
        • For Vertical Take-Off:
          • `L+R-W=0=>R=W-L`..............(1)
        • For Horizontal Take-Off:
          • `T-D-muR=m(dv)/(dt)`
          • By substituting (R)
          • `T-D-mu(W-L)=W/g*(dv)/dt` ...............(2)
    • CONCLUSION:
      • Usually, The Lift-Off Speed is designated to be `1.2 V_(stall)`:
        • `V_(To) = 1.2 V_(stall)`
          • Where `V_(stall)= sqrt((F)/((1/2)*rho*A*C_(L_(max)`
          • Here `C_(L_(max)`is Ground Lift Coefficient For Maximum Take-Off Ground Distance.
  4. TYRE DESIGN:
    1. AIRCRAFT TIRES AND TUBES:
      • Aircraft tires may be tube-type or tubeless. They support the weight of the aircraft while it is on the ground and provide the necessary traction for braking and stopping. The tires also help absorb the shock of landing and cushion the roughness of take-off, rollout, and taxi operations. Aircraft tires must be carefully maintained to perform as required. They accept a variety of static and dynamic stresses and must do so dependably in a wide range of operating conditions.
    2. TIRE CLASSIFICATION:
      • Aircraft tires are classified in various ways including by Type, ply rating, tube-type or tubeless, and bias-ply tires or radials. Identifying a tire by its dimensions is also used. Each of these classifications is discussed as follows.
        1. TYPES:
          • The common classification of aircraft tires is by type as classified by the United States Tire and Rim Association. While there are nine types of tires, only Types I, III, VII, and VIII, also known as Three-Part Nomenclature tires, are still in production.
          • Type I tires are manufactured, but their design is no longer active. They are used on fixed gear aircraft and are designated only by their nominal overall diameter in inches. These are smooth profile tires that are obsolete for use in the modern aviation fleet. They may be found on older aircraft.
          • Type III tires are common general aviation tires. They are typically used on light aircraft with landing speeds of 160 miles per hour (mph) or less. Type III tires are relatively low-pressure tires that have small rim diameters when compared to the overall width of the tire. They are designed to cushion and provide flotation from a relatively large footprint. Type III tires are designated with a two-number system. The first number is the nominal section width of the tire, and the second number is the diameter of the rim the tire is designed to mount upon. [Figure 1]
              • Figure 1. Type III aircraft tires are identified via a two-number system with a (-) separating the numbers. The first number is the tire section width in inches. The second number is the rim diameter in inches. For example, 6.00 – 6 is a Cessna 172 tire that is 6.00 inches wide and fits on a rim that has a diameter of 6 inches

          • Type VII tires are high-performance tires found on jet aircraft. They are inflated to high pressure and have exceptional high load-carrying capability. The section width of Type VII tires is typically narrower than Type III tires. Identification of Type VII aircraft tires involves a two-number system. An X is used between the two numbers. The first number designates the nominal overall diameter of the tire. The second number designates the section width. [Figure 2]

              • Figure 2. A Type VII aircraft tire is identified by its two-number designation. The first number represents the tire’s overall diameter in inches and the second number represents the section width in inches. Type VII designators separate the first and second numbers an “X.” For example, 26 X 6.6 identifies a tire that is 26 inches in diameter with a 6.6-inch nominal width
          • Type VIII aircraft tires are also known as three-part nomenclature tires. [Figure 3] They are inflated to very high pressure and are used on high-performance jet aircraft. The typical Type VIII tire has a relatively low profile and is capable of operating at very high speeds and very high loads. It is the most modern design of all tire types. The three-part nomenclature is a combination of Type III and Type VII nomenclature where the overall tire diameter, section width, and rim diameter are used to identify the tire. The X and “–” symbols are used in the same respective positions in the designator.
              • Figure 3. A Type VIII or three-part nomenclature tire is identified by 3 parameters: overall diameter, section width, and rim diameter. They are arranged in that order with the first two separated by an “X” and the second two separated by a “–.” For example, 18 X 4.25—10 designates a tire that is 18 inches in diameter with a 4.25-inch section width to be mounted on a 10- inch wheel rim.

          • Three-part nomenclature is used on a Type VIII tire, dimensions may be represented in inches or millimeters. Bias tires follow the designation nomenclature and radial tires replace the “–” with the letter R. For example, 30 X 8.8 R 15 designates a Type VIII radial aircraft tire with a 30-inch tire diameter, and 8.8-inch section width to be mounted on a 15-inch wheel rim.

          • A few special designators may also be found for aircraft tires. When a B appears before the identifier, the tire has a wheel rim to section width ratio of 60 to 70 percent with a bead taper of 15 degrees. When an H appears before the identifier, the tire has a 60 to 70 percent wheel rim to section width ratio but a bead taper of only 5 degrees.

        2. PLY-RATING:

          • Tire plies are reinforcing layers of fabric encased in rubber that are laid into the tire to provide strength. In early tires, the number of plies used was directly related to the load the tire could carry. Nowadays, refinements to tire construction techniques and the use of modern materials to build up aircraft tires make the exact number of plies somewhat irrelevant.

          • when determining the strength of a tire. However, a ply rating is used to convey the relative strength of an aircraft tire. A tire with a high ply rating is a tire with high strength able to carry heavy loads regardless of the actual number of plies used in its construction.

        3. TUBE-TYPE OR TUBELESS:

          • As stated, aircraft tires can be tube-type or tubeless. This is often used as a means of tire classification. Tires that are made to be used without a tube inserted inside have an inner liner specifically designed to hold air. Tube-type tires do not contain this inner liner since the tube holds the air from leaking out of the tire. Tires that are meant to be used without a tube have the word tubeless on the sidewall. If this designation is absent, the tire requires a tube. Consult the aircraft manufacturer’s maintenance information for any allowable tire damage and the use of a tube in a tubeless tire.

        4. BIAS-PLY OR RADIAL:
          • The classifying of an aircraft tire is by the direction of the plies used in the construction of the tire, either bias or radial. Traditional aircraft tires are bias-ply tires. The plies are wrapped to form the tire and give it strength. The angle of the plies about direction of rotation of the tire varies between 30° and 60°. In this manner, the plies have the bias of the fabric from which they are constructed facing the direction of rotation and across the tire. Hence, they are called bias tires. The result is flexibility as the sidewall can flex with the fabric plies laid on the bias. [Figure 4]
              • Figure 4. A bias-ply tire has the fabric bias oriented with and across the direction of rotation and the sidewall. Since fabric can stretch on the bias, the tire is flexible and can absorb loads. Strength is obtained by adding plies.

          • Some modern aircraft tires are radial. The plies in radial tires are laid at a 90° angle to the direction of rotation of the tire. This configuration puts the non-stretchable fiber of the plies perpendicular to the sidewall and direction of rotation. This creates strength in the tire allowing it to carry high loads with less deformation. [Figure 5]

              • Figure 5. A radial tire has the fiber strands of the ply fabric oriented with and at 90° to the direction of rotation and the tire sidewall. This restricts flexibility directionally and the flexibility of the sidewall while it strengthens the tire to carry heavy loads

    3. TIRE CONSTRUCTION

      • An aircraft tire is constructed for the purpose it serves. Unlike an automobile or truck tire, it does not have to carry a load for a long period of continuous operation. However, an aircraft tire must absorb the high impact loads of landing and be able to operate at high speeds even if only for a short time. The deflection built into an aircraft tire is more than twice that of an automobile tire. This enables it to handle the forces during landings without being damaged. Only tires designed for an aircraft as specified by the manufacturer should be used.

      • It is useful to the understanding of tire construction to identify the various components of a tire and the functions that contributed to the overall characteristics of a tire. Refer to Figure 6 for tire nomenclature used in this discussion.


          • Figure 6. Construction nomenclature of an aircraft tire.
      • BEAD:

        • The tire bead is an important part of an aircraft tire. It anchors the tire carcass and provides a dimensioned, firm mounting surface for the tire on the wheel rim. Tire beads are strong. They are typically made from high-strength carbon steel wire bundles encased in rubber. One, two, or three bead bundles may be found on each side of the tire depending on its size and the load it is designed to handle. Radial tires have a single bead bundle on each side of the tire. The bead transfers the impact loads and deflection forces to the wheel rim. The bead toe is closest to the tire centerline and the bead heel fits against the flange of the wheel rim.

        • An apex strip is an additional rubber formed around the bead to give a contour for anchoring the ply turn-ups. Layers of fabric and rubber called flippers are placed around the beads to insulate the carcass from the beads and improve tire durability. Chafers are also used in this area. Chafer strips made of fabric or rubber are laid over the outer carcass plies after the plies are wrapped around the beads. The chafers protect the carcass from damage during mounting and demounting of the tire. They also help reduce the effects of wear and chafing between the wheel rim and the tire bead, especially during dynamic operations.

      • CARCASS PLIES:

        • Carcass plies, or casing plies as they are sometimes called, are used to form the tire. Each ply consists of fabric, usually, nylon, sandwiched between two layers of rubber. The plies are applied in layers to give the tire strength and form the carcass body of the tire. The ends of each ply are anchored by wrapping them around the bead on both sides of the tire to form the ply turn-ups. As mentioned, the angle of the fiber in the ply is manipulated to create a bias tire or radial tire as desired. Typically, radial tires require fewer plies than bias tires.

        • Once the plies are in place, bias tires and radial tires each have their own type of protective layers on top of the plies but under the tread of the running surface of the tire. On bias tires, these single or multiple layers of nylon and rubbers are called tread reinforcing plies. On radial tires, an undertread and a protector ply do the same job. These additional plies stabilize and strengthen the crown area of the tire. They reduce Tread distortion under load and increase the stability of the tire at high speeds. The reinforcing plies and protector plies also help resist puncture and cutting while protecting the carcass body of the tire.

      • TREAD:

        • The tread is the crown area of the tire designed to come in contact with the ground. It is a rubber compound formulated to resist wear, abrasion, cutting, and cracking. It also is made to resist heat build-up. Most modern aircraft tire tread is formed with circumferential grooves that create tire ribs. The grooves provide cooling and help channel water from under the tire in wet conditions to increase adhesion to the ground surface. Tires designed for aircraft frequently operated from unpaved surfaces may have some type of cross-tread pattern. Older aircraft without brakes or brakes designed only to aid in a taxi may not have any grooves in the tread. An all-weather tread may be found on some aircraft tires. This tread has typical circumferential ribs in the center of the tire with a diamond-patterned cross tread at the edge of the tire.[Figure 7]

        • The tread is designed to stabilize the aircraft on the operating surface and wears with use. Many aircraft tires are designed with protective undertread layers as described above. Extra tread reinforcement is sometimes accomplished with breakers. These are layers of nylon cord fabric under the tread that strengthen the tread while protecting the carcass plies. Tires with reinforced tread are often designed to be re-treaded and used again once the tread has worn beyond limits. Consult the tire manufacturer’s data for acceptable tread wear and re-tread capability for a particular tire.

            • Figure 7. Aircraft tire treads are designed for different uses.
              • A is a rib tread designed for use on paved surfaces. It is the most common aircraft tire tread design.
              • B is a diamond tread designed for unpaved runways.
              • C is an all-weather tread that combines a ribbed center tread with a diamond tread pattern of the edges.
              • D is a smooth tread tire found on older, slow aircraft without brakes designed for stopping.
              • E is a chine tire used on the nose gear of aircraft with fuselage-mounted jet engines to deflect runway water away from the engine intake(s).
      • SIDEWALL:

        • The sidewall of an aircraft tire is a layer of rubber designed to protect the carcass plies. It may contain compounds designed to resist the negative effects of ozone on the tire. It also is the area where information about the Tire is contained. The tire sidewall imparts little strength to the cord body. Its main function is protection.

        • The inner sidewall of a tire is covered by the tire inner liner. A tube-type tire has a thin rubber liner adhered to the inner surface to prevent the tube from chafing on the carcass plies. Tubeless tires are lined with thicker, less permeable rubber. This replaces the tube and contains the nitrogen or inflation air within the tire and keeps from seeping through the carcass plies.

        • The inner liner does not contain 100 percent of the inflation gas. Small amounts of nitrogen or air seep through the liner into the carcass plies. This seepage is released through vent holes in the lower outer sidewall of the tires. These are typically marked with a green or white dot of paint and must be kept unobstructed. Gas trapped in the plies could expand with temperature changes and cause separation of the plies, thus weakening the tire leading to tire failure. Tube-type tires also have seepage holes in the sidewall to allow air trapped between the tube and the tire to escape. [Figure 8]

            • Figure 8. A sidewall vent marked by a colored dot must be kept free from obstruction to allow trapped air or nitrogen to escape from the carcass plies of the tire
  5. ROLLING RESISTANCE:
    • Rolling resistance sometimes called rolling friction or rolling drag is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. It is mainly caused by non-elastic effects that are, not all the energy needed for deformation (or movement) of the wheel, roadbed, etc., is recovered when the pressure is removed.
    • Two forms of this are:
      1. Hysteresis losses
        • A characteristic of a deformable material such that the energy of deformation is greater than the energy of recovery. The rubber compound in a tire exhibits hysteresis. As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy loss as heat. Hysteresis is the main cause of energy loss associated with rolling resistance and is attributed to the viscoelastic characteristics of the rubber.
      2. Permanent (plastic)
        • deformation of the object or the surface (e.g. soil).
    • NOTE POINT:
      • The slippage between the wheel and the surface also results in energy dissipation. Although some researchers have included this term in rolling resistance, some suggest that this dissipation term should be treated separately from rolling resistance because it is due to the applied torque to the wheel and the resultant slip between the wheel and ground, which is called slip loss or slip resistance. In addition, only the so-called slip resistance involves friction, therefore the name "rolling friction" is to an extent a misnomer.
          • Hard wheel rolling on and deforming a soft surface, resulting in the reaction force R from the surface having a component that opposes the motion.
          • W is some vertical load on the axle, F is some towing force applied to the axle, r is the wheel radius, and both frictions with the ground and friction at the axle are assumed to be negligible and so are not shown.
          • The wheel is rolling to the left at a constant speed.
          • R is the resultant force from non-uniform pressure at the wheel-roadbed contact surface. This pressure is greater towards the front of the wheel due to hysteresis.

    • ROLLING RESISTANCE COEFFICIENT:

      • The "rolling resistance coefficient" is defined by the following equation
        • `F = mu_(rr)*m*g, N`
          • where
            • `mu_(rr) =` Rolling Resistance Coefficient
            • `m =` Mass of the Body
            • `g =` Universal Gravitational
          • where
            • `mu_(rr) = 0.01(1+0.001*V)`

      • Rolling Resistance coefficient `(mu_(rr))`

        coefficient of rolling friction (b)

        Description

        0.0003 to 0.0004

        "Pure rolling resistance" Railroad steel wheel on steel rail

        0.0010 to 0.0015

        0.1 mm

        Hardened steel ball bearings on steel

        0.0010 to 0.0024

        0.5 mm

        Railroad steel wheel on steel rail. Passenger rail car about 0.0020

        0.0019 to 0.0065

        Mine car cast iron wheels on steel rail

        0.0022 to 0.0050

        Production bicycle tires at 120 psi (8.3 bar) and 50 km/h (31 mph), measured on rollers

        0.0025

        Special Michelin solar car/eco-marathon tires

        0.0050

        Dirty tram rails (standard) with straights and curves

        0.0045 to 0.0080

        Large truck (Semi) tires

        0.0055

        Typical BMX bicycle tires used for solar cars

        0.0062 to 0.0150

        Car tire measurements

        0.0100 to 0.0150

        Ordinary car tires on concrete

        0.0385 to 0.0730

        Stagecoach (19th century) on a dirt road. Soft snow on road for the worst case.

        0.3000

        Ordinary car tires on sand
  6. TYRE PRESSURE:
    • To perform as designed, an aircraft tire must be properly inflated. The aircraft manufacturer’s maintenance data must be used to ascertain the correct inflation pressure for a tire on a particular aircraft. Do not inflate to a pressure displayed on the sidewall of the tire or by how the tire looks.
    • Tire pressure is checked while under load and is measured with the weight of the aircraft on the wheels. Loaded versus unloaded pressure readings can vary as much as 4 percent. Tire pressure measured with the aircraft on jacks or when the tire is not installed is lower due to the larger volume of the inflation gas space inside of the tire. On a tire designed to be inflated to 160 psi, this can result in a 6.4 psi error. A calibrated pressure gauge should always be used to measure inflation pressure. Digital and dial-type pressure gauges are more consistently accurate and preferred. [Figure 9]
        • Figure 9. A calibrated bourdon tube dial-type pressure gauge or a digital pressure gauge is recommended for checking tire pressure
    • Aircraft tires disperse the energy from landing, rollout, taxi, and takeoff in the form of heat. As the tire flexes, heat builds and is transferred to the atmosphere, as well as to the wheel rim through the tire bead. The heat from braking also heats the tire externally. A limited amount of heat can be handled by any tire beyond which structural damage occurs.
    • In addition to overheating, underinflated aircraft tires wear unevenly, which leads to premature tire replacement. They may also creep or slip on the wheel rim when under stress or when the brakes are applied. Severely underinflated tires can pinch the sidewall between the rim and the runway causing sidewall and rim damage. Damage to the bead and lower sidewall area is also likely. This type of abuse like any over flexing damages the integrity of the tire and it must be replaced. In dual-wheel setups, a severely underinflated tire affects both tires and both should be replaced.
    • Overinflation of aircraft tires is another undesirable condition. While carcass damage due to overheating does not result, adherence to the landing surface is reduced. Over a long period of time, overinflation leads to premature tread wear. Therefore, overinflation reduces the number of cycles in service before the tire must be replaced. It makes the tire more susceptible to bruises, cutting, shock damage, and blowout. [Figure 10]
        • Figure 10. Tires that are overinflated lack adherence to the runway and develop excess tread wear in the center of the tread. Tires that are underinflated develop excess tread wear on the tire shoulders. Overheating resulting in internal carcass damage and potential failure is possible from flexing the tire beyond design limits
  7. BRAKE FORCES:
    1. Aircraft Brakes:
      • Very early aircraft have no brake system to slow and stop the aircraft while it is on the ground. Instead, they rely on slow speeds, soft airfield surfaces, and the friction developed by the tail skid to reduce speed during ground operation.
      • All modern aircraft are equipped with brakes. Their proper functioning is relied upon for the safe operation of the aircraft on the ground. The brakes slow the aircraft and stop it in a reasonable amount of time. They hold the aircraft stationary during engine run-up and, in many cases, steer the aircraft during taxi.
        • working of Aircraft Brakes:
          • In the typical brake system, mechanical or hydraulic linkages to the rudder pedals allow the pilot to control the brakes.
          • Pushing on the top of the right rudder pedal activates the brake on the right main wheel(s) and pushing on the top of the left rudder pedal operates the brake on the left main wheel(s).
        • Operation of Aircraft Brakes:
          • The basic operation of brakes involves converting the kinetic energy of motion into heat energy through the creation of friction.
          • A great amount of heat is developed and forces on the brake system components are demanding.
          • Proper adjustment, inspection, and maintenance of the brakes are essential for effective operation.

QUESTION-6:

  • TAKE SOME NECESSARY ASSUMPTIONS AND CALCULATE THE FORCE AND POWER REQUIRED TO PUSH AND PULL AN AIRCRAFT BY A TOWING VEHICLE.

ANSWER-6:

  • The force acting on an aircraft during the push and pull of the towing vehicle are rolling resistance and air drag force. The Hill climbing force is Neglected for the reason of " the runways are constructed in flat surface and No gradient ratio is required.

CALCULATION:

  • Let assume an Aircraft of Airbus A380-800 plane
    • Mass of the Aircraft `m_1 =`575000 `Kg`
    • Mass of the Towing Vehicle `m_2`= 55000 `Kg`
    • Coefficient of Rolling Ground friction for Dry Concrete or Asphalt road `mu_(rr) =`0.03`
    • Frontal Area of the Vehicle `A = 37,m^2.`
    • Drag Coefficient of an aircraft `C_(d_A)`(aircraft) = 0.5
    • Drag Coefficient of a Trowing Vehicle `C_(d_T)` (Towing) = 0.16,
    • Density of Air =`1.225, kgm^3`
    • Universel Gravity value `g = 9.81, ms^2`
    • Speed of an Aircraft V = `20,kmph=20*(5/18)=5.556,ms^-1,`
      • ROLLING RESISTANCE FORCE:
        • FOR THE AIRCRAFT:
          • `F_(rr)(aircraft) = mu_(rr)*m*g=0.03*57500*9.81`
          • `F_(rr)(aircraft) =169,222.5,N` ......................(1)
        • FOR THE TOWING VEHICLE:
          • Towing vehicle`F_(rr)(Vehic)=mu_(rr)*m_2*g=0.03*55000*9.81`
          • `F_(rr)(Vehic)= 16,186.5,N` ......................(2)
        • we need to added the mass of the aircraft & an Towing Vehicle for pushing and pulling the aircraft so TOTAL ROLLING RESISTANCE FORCE `F_(rr(A&T)`:
          • `F_(rr(A&T) = F_(rr)(aircraft)+F_(rr)(vehic)`
          • `F_(rr(A&T) = 169222.5+16186.5`
          • `F_(rr(A&T) = 185,409.N`
      • AERODYNAMIC DRAG FORCE:
        • `F_(ad)=(1/2)*rho*A*V^2*(C_(d_A)+C_(d_T))`
        • `F_(ad)=(1/2)*1.225*37*(5.556)^2*(0.5+0.16)`
        • `F_(ad)=461.71N`
    • Here HILL CLIMBING FORCE is neglected due to the surface of the runway area is a flat surface and gradient percentage is ZERO
      • TOTAL TRACTION FORCE:
        • `therefore`Total Traction Force required to pull and push the aircraft by the Towing Vehicle is:
          • `F=F_(rr)(A&T)+F_(ad)`
          • `F=185409+461.71`
          • `F=185,870.71,N`
      • TOTAL POWER:
        • The total power required to pull and push the aircraft by the Towing Vehicle is:
          • `P =F*V`
          • `P=185870.71*5.556`
          • `p=1032697.66`watts
          • `P=1032697.66/1000=1032.69kw`
          • `P=1032.69kw`
  • RESULT:
    • THE TOTAL FORCE AND TOTAL POWER REQUIRED TO PULL AND PUSH THE AIRCRAFT BY THE TOWING VEHICLE IS:
      • TOTAL FORCE (F) = 185,870.71,N
      • TOTAL POWER (P) = 1032.69kw
  • The Excel Sheet Calculation for both the FORCE and POWER is shown below:
  • THE SIMULINK MODEL FOR BOTH FORCE AND POWER REQUIRED TO PULL AND PUSH THE AIRCRAFT BY THE TOWING VEHICLE SHOWN BELOW:
      • A subset of Rolling resistance Force Calculation
      • A subset of Aerodynamic Drag Force Calculation

QUESTION-7:

  • DESIGN AN ELECTRIC POWERTRAIN WITH THE TYPE OF MOTOR, ITS POWER RATING, AND ENERGY REQUIREMENT TO FULFILL AIRCRAFT TOWING APPLICATION.
    • MAKE ALL REQUIRED ASSUMPTIONS.
    • ESTIMATE THE DUTY CYCLE RANGE TO CONTROL THE AIRCRAFT SPEED FROM ZERO TO HIGHEST.
    • PREPARE A TABLE OF ASSUMED PARAMETERS.
    • DRAW A BLOCK DIAGRAM OF THE POWERTRAIN.

ANSWER-7:

  • DESIGN AN ELECTRIC POWERTRAIN WITH THE TYPE OF MOTOR, ITS POWER RATING, AND ENERGY REQUIREMENT TO FULFILL AIRCRAFT TOWING VEHICLE APPLICATION:
    • AIRCRAFT TOWING VEHICLE APPLICATION:

  • DESIGN AN ELECTRIC POWERTRAIN BY SIMULINK MODEL:
      • WORKING OF SIMULATION DESIGN MODEL OF TOWING VEHICLE APPLICATION:
        • The above Simulation model explains the work of a Towing Vehicle Which consisted of Longitudinal driver Block, Controllers, Duty cycle, Vehicle structure and Performance.
        • Longitudinal Diver Block Acts As The control of Acceclaration and Breaking System That is controlled by Driver
        • Duty cycle is the Time duration of the vehicle accelerated and stop in the present time.
        • Controller Block deals to control all the components of the vehicle system.
      • RESULTS OF SIMULATION TOWING VEHICLE
  • REQUIRED ASSUMPTIONS
      • Calculating The Efficiency Of Motor by input energy and output energy:
        • Lets calculate the values of output energy for 120 min
          • Output Energy `E_(out) = P_(out)* t`
            • Where, `P_(out) =`Output Power, `t=`Time Period = 120 min
          • So Here `P_(out)=1033,kw`& `t = 120,min=120*1/3600,hr`
            • `E_(out) = P_(out)*t=1033*120/3600`
            • `E_(out)=34.433,kwh` ..............................(3)
        • Lets calculate the values of input energy for 120 min
          • Input power `P_(In)`Is Taken From Above Moter Power Rating Configuration As 1060,kw
            • The Input Power is calculated from rated voltage and rated current
            • `P_(In)= V_(r)*I_(r)` here `I_(r) = 500,amps` & `V_(r) = 2120, kv`
            • `P_(In)= 2120*500`
            • `P_(In)=1060,Kw` .........................(*)
            • So Input Power `P_(In)=1060,kw`
          • Input Energy `E_(In) = P_(In)* t`
            • Where, `P_(In) =`Input Power, `t=`Time Period = 120 min
          • So Here `P_(In)=1060,kw`& `t = 120,min=120*1/3600,hr`
            • `E_(In) = P_(In)*t=1060*120/3600`
            • `E_(In)=35.33,kwh` ..............................(4)
        • The Efficiency Of Motor by input energy and output energy calculated as :
          • From eq (3) & (4)
          • `eta = E_(out)/E_(In)*100`
          • `eta=34.43/35.33*100`
          • `eta = 97.4%`
      • So The Efficiency Of the Motor Is Satisfied by The above Assumptions of `eta=97.4%`
  • ESTIMATE THE DUTY CYCLE RANGE TO CONTROL THE AIRCRAFT SPEED FROM ZERO TO HIGHEST.
    • The Duty cycle is calculated by Output power and Input Power Values, Now the Values are Mentioned Above:
      • Output Power `P_(out) = 1033, kw`and Input Power `P_(In)=1060, kw`
      • The Duty cycle is denoted by D
      • The Duty Cycle `D=P_(out)/P_(In)*100`
      • `D=1033/1060*100=97.4%`
      • The DUTY CYCLE (D) = 97.4%
    • So THE DUTY CYCLE RANGE TO CONTROL THE AIRCRAFT SPEED FROM `0`to `97.4%`
  • DRAW A BLOCK DIAGRAM OF THE POWERTRAIN BLOCK OF TOWING VEHICLE APPLICATION

REFERENCE LINK:

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